1. Field of Endeavor
The present invention relates to the technology of gas turbines, and more particularly to a method for repairing a gas turbine component.
2. Brief Description of the Related Art
Today, gas turbines have operation temperatures of more than 1000° C. Accordingly, the components of those gas turbines such as blades, vanes or liners are exposed to a high thermal load and mechanical stress. As those components are usually made of expensive high-temperature materials, it is desirable to repair those components, when damaged, instead of replacing them. However, the repair of damaged gas turbine component is difficult, when the damaged section is removed and an insert is manufactured to fit into the removed region, as the insert has to be manufactured with high precision to avoid a loss in mechanical stability and change in the flow characteristics of the machine.
The document EP 1 231 010 A1 discloses a method of repairing gas turbine engine components. The method includes removing the damaged portion and fabricating an insert to match the removed portion. The insert is precision machined and crystallographically matched to the original component, and then bonded to this component using transient liquid phase bonding techniques and suitable heat treatment. Although the document contains a wealth of information on the bonding process, no details of the precision machining of the insert are given.
The disclosure of document EP 1 620 225 B1 relates to a method for repairing and/or modifying components of a gas turbine. Initially, at least one particularly damaged section of the component, which is to be repaired, is extracted from the component. A 3-D data set is then produced for the replacement part, which is to be produced, if not available. The replacement part is subsequently produced with the aid of a rapid manufacturing process. Finally, the produced replacement part is integrated into the component, which is to be repaired. As the rapid manufacturing process is not adaptive, the precision is limited.
According to U.S. Pat. No. 5,269,057, a method for replacing airfoil components includes the steps of identifying a portion of the airfoil to be replaced, removing the portion by a nonconventional machining process, such as continuous wire electrical discharge machining, and forming a replacement member utilizing a similar cutting process. A cutting path utilized to remove the portion to be replaced and to form the replacement member includes interlocking projections and sockets and may include one or more tapers along the cutting path so that the portion may be removed only by lifting in one direction. For the cutting, an electrical discharge cutting wire moves along the outside of a CNC programmed cutting path. Again, the manufacturing process for the insert is not adaptive, which limits the precision.